Venous blood will be drawn from 1250 subjects. It is expected that 25% will have obstruction that is poorly responsive to albuterol and require admission to hospital for resolution. The other 75% will have obstruction that quickly resolves with albuterol and who are discharged home. The DNA will be isolated and assayed blindly by the Center for Human Genetics Research, Vanderbilt Medical Center for identification of β2 AR SNPs at positions 16 and 27 and receptor haplotypes. Single-nucleotide polymorphisms will be genotyped by use of TaqMan single-nucleotide polymorphism genotyping assays (Applied Biosystems, Foster City, CA, USA). Eleven polymorphisms will be selected for genotyping from within the ADRB2 coding region and up to about 5 kb 5' Codon 1 (rs11958940, rs17778257, rs2895795, rs2053044, rs12654778, rs11959427, rs1042711, rs1042713, rs1042714, rs1800888, and rs1042718). Quality-control measures include a genotype call rate of 95% and no significant departures from Hardy-Weinberg Equilibrium within each racial group (exact p value > 0.01). Haplotypes will be predicted with publicly available software (SNPHNP-a program for estimating frequencies of large haplotypes of single-nucleotide polymorphisms [version 1.3]). Haplotype pairs 2/2, 2/4, 2/6, 4/4, 4/6 and 6/6 will be evaluated.